The metal binding sites of a large number of metalloproteins contain imidazole rings from histidyl residues of the protein. Examination of the structural data available for these proteins suggests that the ability of these metal-bound imidazole rings to hydrogen bond using the N-H group of the pyrrole nitrogen or to be deprotonated to form a bridge between two metal ions is an important aspect of their chemistry. We propose to continue our studies of the chemistry of the N-H functionality in imidazole complexes and in metalloprotein copper-zinc superoxide dismutase. Studies of model compounds will have as their goal the synthesis and characterization of new complexes of imidazole, of imidazole derivatives that are internally hydrogen bonded, of imidazolate, and of imidazolate derivatives that are sterically blocked to prevent binuclear complex formation. Particular emphasis will be placed on synthesis of new imidazole and imidazolate complexes of iron porphyrins in order that the information derived from these studies may be related to structural and chemical properties of hemoproteins. Studies of Cu-Zn superoxide dismutase will focus on elucidating the kinetics and thermodynamics of the metal binding or metal rearrangement reactions of the apoprotein, the native protein, and partially substituted derivatives using copper, zinc, and other metal ions. The goal of this research is to understand the bonding of metals ions in the many metalloproteins and metalloenzymes in which histidyl residues play an important role. Such information will enhance our understanding of the mechanism of action of a variety of metalloproteins and metalloenzymes important to human health such as hemoglobin, myoglobin, catalase, cytochromes, superoxide dismutase, etc.